Method and apparatus for continuously producing solutions and suspensions

ABSTRACT

A novel method and apparatus for continuously producing chemical solutions and suspensions is disclosed. The novel invention serves to effect a continuous dissolving process of a chemical solute in a solvent and does so in a fashion which prevents the formation of agglomerates and jellylike skin on the particles and serves to dissolve or suspend such materials without introducing high sheer force into the product. In a preferred embodiment, the novel invention contemplates to effect a high-speed whirling or fluffing of the particles and, at the same time, to impart a positive downward movement thereto. The solvent is then sprayed into the whirling mass at different stepwise spaced locations along the direction of downward movement of the particles, which particles or mass, now full wetted, are then continuously agitated at a relatively low speed providing mild agitation and kneading and a dwell time sufficient for the time required for the dissolving or suspension reactions to complete.

United States Patent Gresch et a1. Mar. 7, 1972 [54] METHOD AND APPARATUS FOR [56] References Cited CONTINUOUSLY PRODUCING SOLUTIONS AND SUSPENSIONS UNTED STATES PATENTS Inventors: Walter Gresch Muttenz; Horst Pilch Pm 3,160,352 12/1964 Mollrmg ..241/98 :13; nlilrwm Ruttener, Rihen, all of Swit- Primary Examiner Theodore M orris Attorney- Jacobi, Davidson & Kleeman [73] Assignee: Buss AG, Basel, Switzerland 221 Filed: Nov. 12,1969 [57] ABSIMCT I A novel method and apparatus for continuously producing [21] App! 875962 chemical solutions and suspensions is disclosed. The novel in- Rehned s Appucafion Data vention serves to effect a continuous dissolving process of a chemical solute in a solvent and does so in a fashion which [63] commuatlonm'part of 5 prevents the formation of agglomerates and jellylike skin on 1966- the particles and serves to dissolve or suspend such materials without introducing high sheer force into the product. In a [30] Formal Apphcauon Pnonty Dam preferred embodiment, the novel invention contemplates to Dec. 20, 1965 Switzerland 1 7696/65 effect a high-Speed whirling or fluffing of the Particles and, at the same time, to impart a positive downward movement [52] US. Cl ..l06/l87, 106/198, 260/326, thereto- Th S lv nt is then sprayed into the whirling mass at 260/32.8,260/34.2 different stepwise spaced locations along the direction of [51] Int. Cl. ..C08b 27/48 downward movement of the particles, which particles or m [58] Field of Search ..241/l2, 16; 260/342; 106/187, now full wetted, are then continuously agitated at a relatively 106/ 198 low speed providing mild agitation and kneading and a dwell time sufficient for the time required for the dissolving or suspension reactions to complete.

3 Claims, 1 Drawing Figure PAIENTEDMAR 7:912

S E R N 03 F. E T N Gum v WEN URW AOR WHE METHOD AND APPARATUS FOR CONTINUOUSLY PRODUCING SOLUTIONS AND SUSPENSIONS This application is a continuation-in-part of application Ser. No. 600,538, filed Dec. 9, 1966.

BACKGROUND OF THE INVENTION This invention generally relates to a method and apparatus for continuously producing chemical solutions and suspensions and particularly concerns a method and apparatus wherein a continuous dissolving process is carried out with those materials wherein difficulties previously have been experienced in overcoming agglomerate formation between the solid and the solvent and wherein the solvent tended to form a jellylike skin which had to be rubbed off so as to expose new particle surfaces for the solvent penetration.

Continuous dissolving processes of the general type above described have been carried out in the prior art by means of the employment of screw extruders and the like. Yet, it has been found that with such prior art techniques and associated apparatus, a significant disadvantage occurs in that when dosing the particles to be dissolved or suspended, large agglomerates oftentimes form in the vicinity of the feed inlet. These agglomerates were enveloped by solvent and a jellylike skin formed over the agglomerates which hindered further dissolving. Thus, the jellylike skin of the agglomerates had to be rubbed off so as to expose a new surface for the penetration of the solvent and, to rub off such skin, relatively large sheer forces had to be provided which required complicated apparatus oftentimes utilizing special abrading elements. The same difficulties were seen to arise in the prior art when suspensions rather than solutions were produced in accordance with the prior art techniques. As a result, such prior art techniques were highly inefficient and the apparatus required to carry out such techniques were expensive, required relatively high operational power and generally were uneconomical.

SUMMARY OF THE INVENTION Thus, a need exists in the art for a new and improved method as well as apparatus for continuously producing chemical solutions and suspensions in a manner eliminating the disadvantageous aspects associated with prior art techniques and devices. It is a primary object of the instant invention to provide such a new and improved method and apparatus.

Further, more specific yet equally important objects of the instant invention concern the provision of a novel method and apparatus which continuously produces solutions and suspensions, which method and apparatus operates without the necessity of introducing high sheer forces into the product. An additional object of the instant invention concerns the provision of a new and improved method and apparatus of the type described which serves to prevent the formation of agglomerates and further serves to prevent the formation of a jellylike skin by the solvent over the solid solute particles. Another significant object of the instant invention concerns the provision of a new and improved method and apparatus of the described general type which operates in an efiicient and highly economical fashion.

These objects as well as other objects which will become apparent as the description proceeds, are implemented by the novel invention which takes the form of both a method and apparatus operative to continuously produce chemical solutions and suspensions. The novel invention is characterized by the features that the solid particles are whirled at high speed and are fiuffed while, at the same time, a positive downward movement is imparted thereto. Now, the solvent is sprayed into the whirling mass at stepwise, spaced locations along the direction of movement of the mass, which mass, now fully wetted, is subsequently mildly continuously agitated and kneaded at a relatively low speed for a length of time corresponding to the time required for the dissolving or suspension reactions to complete. In the preferred inventive embodiment, the difference in speed between the high-speed whirling or fluffing procedure and the low-speed continuous mild agitation and kneading represents a 66.6 multiple although at least a tenfold multiple has been found to be sufficient.

The novel apparatus for carrying out the method above discussed is contemplated to comprise a continuous kneader means operating at a given relatively low r.p.m. such as 45 r.p.m., for example. A continuous mixer means is disposed upstream of the kneader means and serves to form a solution free from agglomerates of solids and liquids and serves to feed the solution to the kneader means. Separate inlet means are associated with the mixer means and serve to deliver the solids and liquids to the mixer means with the mixer means, in the preferred embodiment, comprising a housing and a shaft disposed within the housing, the shaft incorporating a plurality of mixing and comminuting elements spaced along the length thereof. Finally, means for driving the shaft at a considerably higher multiple r.p.m. than the rpm. of the kneader means are provided such that the solids and liquids fed thereto are rapidly whirled and such that the solids are, in fact, fluffed. In the preferred inventive embodiment, such shaft is contemplated to be driven at approximately 3,000 rpm.

BRIEF DESCRIPTION OF THE DRAWING The invention itself both from its method as well as apparatus aspects, will be better understood and further features and advantages thereof will become apparent when attention is given the following detailed description of a preferred inventive arrangement, such description referring to the appended single sheet of drawing wherein the sole FIGURE thereon schematically depicts an elevational view, partially in cross section, of a novel apparatus suitable for carrying out the novel improved method.

DETAILED DESCRIPTION OF THE PREFERRED INVENTIVE EMBODIMENT Now, by referring to the drawing, the detailed structure of the novel apparatus will be apparent and, by an understanding of such apparatus and the operation thereof, the novel features of the improved method for continuously producing solutions and suspensions will be appreciated.

The preferred arrangement or apparatus for continuously producing solutions or suspensions will be seen to comprise a continuous kneader 1 having a housing 2 in which is disposed a rotatable worm 3 driven at a relatively low r.p.m., such as 45 r.p.m., for example, by means of a motor 4 and suitable adjustable gearing disposed in housing 4.

A high-speed mixer 5 is provided and has a discharge opening 6 coupled with the feed opening of the housing 2 of the continuous kneader 1. The high-speed mixer incorporates a vertical housing 7 in which a shaft 8 is disposedv As is illustrated, shaft 8 incorporates a series of mixing and comminuting elements 9 spaced along the shaft length and which project radially outward therefrom. An electric motor 10 is provided and is coupled with the end of the shaft extending above the top end of a housing 7, electric motor 10 driving the shaft at a relatively high speed, such as 3,000 rpm, for example. Accordingly, the rpm. of shaft 8 thus comprises a considerably higher multiple than that of the worm 3 and, in the example given, will be seen to turn 66.6 times faster than the worm although at least a tenfold multiple has been found to be suitable.

The solid matter or solute which is to be dissolved in the liquid or solvent is initially contained in a hopper l1 and is delivered, in metered amounts, to an inlet 13 disposed in the upper portion of the mixer by means of an endless belt or weigh feeder 12. The solid matter which at this time has become pulverized is engaged by the winglike mixing and comminuting elements 9 and specifically is initially. engaged by the comminuting element provided on the shaft in the region of the inlet opening. Due to the high speed of revolution of the shaft 8, the solid matter is caused to be rapidly whirled or rotated and actually fluffed whereby relatively loose agglomerates of the solid or solute are broken up. At the same time, the fluffed, rapidly whirling particles have a positive downward movement imparted thereto due to the combined effect of gravitational force and the construction of the mixing and comminuting elements 9.

Liquid or solvent is delivered from a container 14 through a feedpipe l5 and dosing or metering pump 17 to the vertical housing 7 of the mixer. In the preferred inventive embodiment as is illustrated, feedpipe 15 has a plurality of outlets stepwise spaced along the circumference of housing 7 in the direction of downward movement of the whirling particles. The discharge of the liquid or solvent in this fashion into the whirling mass serves to fully wet the mass as the whirling mass is positively, or under gravitational force, driven downwardly. To reinforce the agglomerate breaking action, the inside surface of the walls of housing 7 is preferably provided with stationary elements 16 having a wedgelike cross section, these stationary elements cooperating with the mixing and comminuting elements 9.

Now, the wetted mass or mixture enters the continuous kneader 1 through discharge opening 6 of the mixer housing 7 and such mixture can be further processed without difficulty. Specifically, while in the continuous kneader, the wetted mass is mildly but continuously agitated and kneaded with a dwell time corresponding to the time required for the dissolving or suspension reactions to complete. This is a generally wellknown dwell time requirement even for fully wetted particles with complete solvent penetration where, in many cases, materials will pass through intermediate physical stages of gel formation with higher viscosity and where some mild kneading is sufficient, provided no undissolved particle agglomerates are present. As a further advantageous feature, housing 7 preferably has a separate inlet for each of the substances to be mixed together.

The above-described arrangement is, for example, particularly suitable for dissolving polyacrylo nitrile in dimethylformamide, acetyl cellulose in acetone, PVC in cycle-hexanone, for example, and for producing suspensions from terephthalic acid and glycol, for example, whereby the time that the product is in the arrangement for continuously producing solutions and suspensions as against that spent in a batch operating arrangement, is appreciably shorter. As a consequence, the quality of the product is improved and, when dissolving polyacrylo nitrile in dimethylformamide, for example, the yellowing which otherwise appears, is greatly reduced or even altogether eliminated.

In one particular preferred process wherein clear spinning solutions of polyacrylo nitrile in dimethylformamide as solvent was produced, the resulting spinning solution was seen to have optimum light color and clarity and was free of any gel particles rendering a final product having the desired properties.

The polyacrylo nitrile polymer, in the form of a very fine powder having a tendency to shooting and bridging was continuously proportioned at a rate of approximately 200 kg./hr. into the inlet 13 of the high-speed mixer 5 wherein it was fluffed and whirled and given a downward feed by the mixing and comminuting member 9' in the inlet throat. 800 kg./hr. of the solvent was stepwise added through the spray nozzles 15. The high-speed mixer was driven at a rate of 3,000 r.p.m. and the material rapidly passing through was instantaneously dissolved with the product temperature rising from the ambient only to about 40 C. The housing 7 of the high-speed mixer 5, in this exemplary operation, was cooled by water at ambient temperature and it was noted that the absorbed power was only approximately 10 hp.

The dissolved product then passed into the continuous kneader 1 through the discharge opening 6 of the high-speed mixer 5 and entered such kneader at the rate of 1,000 kg./hr. At this time, the dissolved product in this exemplary arrangement, was slightly heated to below C. and was agitated for the stabilization of the solution. The kneader pocket and the internal worm or screw lpreferably was heated to C. from an external steam supp y and the screw was run at 42 r.p.m.

absorbing 32 hp. The average processing time from feeding the dry and liquid components into the apparatus to the time that the clear spinning solution left the kneader was approximately 3 minutes.

As should now be apparent, the objects initially set forth at the outset of the specification have been successfully achieved. Accordingly,

What is claimed is:

l. A method for continuously producing chemical solutions and suspensions, such method comprising the steps of:

delivering into a mixer means a metered dose of solid solute particles in a finely comminuted condition;

fluffing the solid finely comminuted particles by whirling same at a first speed and imparting to the solid particles a positive downward movement; introducing a metered dose of solvent into the whirling, downwardly moving, finely comminuted particles whereby the whirling mass is wetted only to the extent that there are formed loose agglomerates of such particles; further whirling the wetted loose agglomerates and in such condition further comminuting the, loose agglomerates;

said first speed at which said particles are whirled being at least 10 times greater than said second speed at which the wetted further comminuted agglomerates are mildly continuously agitated and kneaded;

then mildly continuously agitating and kneading the wetted further comminuted agglomerates at a second speed considerably lower than said first speed and for a given dwell time; and

discharging the product.

2. A method as defined in claim 1, including the step of introducing the metered dose of solvent at a plurality of locations along the path of downward movement of the whirling mass.

3. A method as defined in claim 2, including the step of mixing and comminuting the downwardly moving whirling mass during such time as the metered dose of solvent is introduced therein. 

2. A method as defined in claim 1, including the step of introducing the metered dose of solvent at a plurality of locations along the path of downward movement of the whirling mass.
 3. A method as defined in claim 2, including the step of mixing and comminuting the downwardly moving whirling mass during such time as the metered dose of solvent is introduced therein. 